Go beyond the foot-candle numbers. This guide provides electricians with the practical steps to use IES photometric data for anticipating beam direction, confirming mounting points, and helping ensure a high-performing aisle-optic high bay installation. It translates technical data into an on-site checklist designed to help prevent common installation errors.
Disclaimer: This guide provides general recommendations for lighting installation based on industry best practices. All work must be performed by a qualified, licensed electrician in strict accordance with the National Electrical Code (NEC®), specifically NFPA 70, all applicable local building codes, and project-specific contractual documents. The authors and publisher are not liable for any damages or injuries resulting from the use or misuse of this information.
IES files are more than just design tools; for an electrician in the field, they serve as a technical blueprint. Overlooking these files—especially with specialized aisle-optic fixtures—is a frequent cause of poor site performance. A layout that appears correct on a 2D floor plan can underperform significantly if the fixtures are rotated 90 degrees off-axis. This guide leverages field experience to help you align the physical installation with the intended lighting design.
From Screen to Site: Reading IES Data for Installation
The first step is understanding what the data represents. An IES file, standardized by the IES LM-63-19 (IES Standard File Format for the Electronic Transfer of Photometric Data), is a text-based data set containing a 3D map of a light fixture's intensity. For an installer, the most actionable part of this data is the polar plot, or candela distribution graph.

The Polar Plot: Your On-Site Beam Map
The polar plot provides a cross-sectional view of the light beam. While a standard UFO high bay typically shows a circular, symmetrical plot, an aisle-optic fixture will display an elongated "batwing" or oval shape. This distribution is engineered to project light along the length of a warehouse aisle rather than onto the tops of storage racks.
To apply this on-site, visualize the elongated axis of the plot as the primary path of the light. This axis must align with the center-line of the aisle to meet the design's foot-candle requirements.
Finding the 0-Degree Axis: The Most Critical Step
The polar plot is oriented on a 0-degree to 180-degree axis. In the IES standard, this 0-degree plane corresponds to a specific physical orientation of the luminaire.
- Identification: Look for a physical marker on the fixture housing, such as a molded arrow, a notch, or the orientation of the mounting bracket.
- Common Error: Based on field observations in narrow-aisle warehouse projects, installing fixtures 90 degrees off-axis can reduce center-line illuminance by 50% or more. In these cases, the peak intensity is directed into the racking, creating glare for operators and leaving the floor in shadow.
- Verification: Before hanging the first row, verify which physical feature represents the 0° mark. If the fixture lacks a clear mark, refer to the manufacturer’s installation sheet or the "Luminous Opening" section of the IES file.
The Aisle-Optic Pre-Install Checklist
Follow this systematic process to ensure the photometric design is accurately executed.
Step 1: Match the IES File to the Physical Fixture
Before starting the lift, compare your materials with the design documents.
- Verify Model Codes: Ensure the IES file matches the exact wattage and optic code (e.g., "60x120 degree") of the fixtures on the pallet.
- Use a Viewer: Open the file in a free IES viewer (such as the IES Photometric Toolbox or online viewers). Confirm that the "long" part of the beam aligns with the 0-180° axis.
- Mark the Fixture: If the 0° mark is hard to see from a lift, use a high-visibility paint pen to mark the "aisle-facing" side of the housing for the crew.
Step 2: Verify Mounting Height and Spacing Ratios
The IES data dictates the optimal spacing to ensure uniformity. A key metric is the Spacing-to-Mounting-Height (S/MH) ratio.
- Field Rule of Thumb: For high-rack aisles (25–40 ft mounting heights), an S/MH ratio between 0.6 and 1.1 is common for achieving the uniformity suggested in ANSI/IES RP-7-21, Section 6.
- Calculation: If fixtures are mounted at 30 feet, they should typically be spaced between 18 and 33 feet apart.
- Red Flag: If the site plan shows spacing significantly wider than 1.2 times the mounting height, consult the project manager. Excessive spacing often results in "strobe effect" lighting, where light levels drop significantly between fixtures. For more on this, see our guide on achieving lighting uniformity in a warehouse layout.
Step 3: Confirm Peak Candela and Beam Alignment
The "peak candela" is the point of maximum light intensity. In aisle optics, this is focused to penetrate deep into the aisle.
- Alignment: Ensure the peak intensity is aimed precisely down the center-line.
- Tilt Limits: Some brackets allow for minor tilting (e.g., 10°). Per manufacturer guidelines, these are for leveling, not for correcting poor placement.
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Quick Spot Check: You can estimate the expected light level using the Inverse Square Law:
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Formula:
E (fc) = I (cd) / [h (ft)]² -
Example: If the IES file shows a peak of 30,000 cd and the height is 30 ft, the estimated initial foot-candles directly under the fixture is:
30,000 / 900 = 33.3 fc.
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Formula:
Step 4: Account for the Light Loss Factor (LLF)
Lighting designs include a Light Loss Factor (LLF) to account for dust and LED aging, typically ranging from 0.70 to 0.85 in industrial settings.
- Expectation: Initial readings should be roughly 20-30% higher than the target levels on the design plan. If the plan calls for 20 fc maintained, seeing 26 fc on day one is normal and expected to ensure long-term compliance with ANSI/IES RP-7-21 safety standards.
Field Verification and Common Pitfalls
Commissioning with a Lux Meter: Documentation
Use a calibrated lux meter to verify the installation. For a valid sample, take measurements at 10-foot intervals along the aisle center-line.
Example Field Measurement Log:
| Location | Target (Maintained) | Initial Design (Target x 1.2) | Measured (Actual) | Result |
|---|---|---|---|---|
| Under Fixture A | 20 fc | 24 fc | 27 fc | Pass |
| Midpoint (A & B) | 15 fc | 18 fc | 19 fc | Pass |
| Under Fixture B | 20 fc | 24 fc | 26 fc | Pass |
| Note: | Measured at 36" AFF |
Wiring and Control Safety
Modern installations require strict adherence to NEC Article 725 for Class 2 dimming circuits (0-10V).
- Safety Protocol: Before wiring, de-energize the circuit. Follow OSHA 1910.147 Lockout/Tagout (LOTO) procedures. Use a verified non-contact voltage tester to confirm the absence of voltage.
- Polarity: 0-10V dimming is polarity sensitive. Purple (Dim+) and Pink/Gray (Dim-) wires must be consistent across the run.
- Circuit Loading: Avoid exceeding the maximum sink current of your occupancy sensors. Typically, a single sensor should not control more than 20–30 drivers, but always check the sensor's spec sheet.
For high-performance fixtures like the Hyperlite LED High Bay Light - Black Hero Series, which supports 0-10V dimming, correct wiring is essential for the system to reach its rated efficiency.
Key Takeaways for the Field
- Orientation: Always align the fixture's 0-degree mark with the aisle length.
- Verify Height: Confirm the actual mounting height matches the IES file's assumptions.
- Document: Keep a log of initial foot-candle readings as an "as-built" record for the client.
- Standards: Reference ANSI/IES RP-7-21 for industrial lighting requirements and NEC Article 725 for control wiring.
References and Standards
- ANSI/IES RP-7-21: Recommended Practice: Lighting Industrial Facilities. (Focus on Table 6.1 for warehouse illuminance).
- IES LM-63-19: Standard File Format for the Electronic Transfer of Photometric Data.
- NFPA 70 / NEC Article 725: Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits.
Frequently Asked Questions (FAQ)
How can I view an IES file on a smartphone?
Several mobile apps and web-based "IES viewers" allow you to upload a .ies file to see the polar plot. This is a highly effective way to verify beam shape while on a lift.
What happens if I rotate an aisle-optic fixture by 90 degrees?
In most narrow-aisle applications, this results in a "fail." The light is directed into the racks, often causing a 40-60% drop in floor illuminance and creating significant glare for equipment operators.
Why are my foot-candle readings higher than the plan?
This is usually due to the Light Loss Factor (LLF). Designers plan for the "worst-case" scenario (end of life/dirty fixtures). New, clean fixtures should read 20-30% higher than the maintained target.
Can I use a standard UFO high bay instead?
While possible, it is generally less efficient. Symmetrical UFO lights waste light on top of racks. Aisle-optic fixtures, as discussed in our guide to high-rack vertical illumination, focus the lumens where they provide the most value for safety and productivity.